20 



NATURE 



[May I, 1890 



Tuatera Lizard {Sphenodon punctalus) from New Zealand, pre- 

 sented by Mr. J. Catheson Smith ; an Ej;yptian Ichneumon 

 {Herpestes ichneumon) from North Africa, two Grey Ichneumons 

 {Herpestes griseus $6), two Alexandrine Parrakeets {PalcEornis 

 alexandri) from India, two White Pelicans {Pclecanus onocro- 

 talus), .South European, deposited ; a Musk Deer {Moschus 

 moschiferus $ ) from Central Asia, seven Bearded Lizards 



{Amphibolurus barbatus), three Lizards {Amphibolurus 



muricatus), a Gould's Monitor ( Varanus goulJi) from Australia, 

 purchased ; a Barnard's Parrakeet {Platycercus barnardi) from 

 South Australia, received in exchange ; an Indian Muntjac 

 {Cervulus muntjac), born in the Gardens. 



OUR ASTRONOMICAL COLUMN. 

 Objects for the Spectroscope. 

 Sidereal Time at Greenwich at 10 p.m. on May i = 

 I2h. 39m. 6s, 



Remarks. 



(1) During his spectroscopic survey of nebulas in 1868, Lieut. 

 Herschel noted that this gave a bright line spectrum. The 

 three principal nebular lines and G were observed, but, as I 

 have before remarked, other lines may possibly ht found if 

 carefully looked for. Some of the lines observed in other 

 nebulse, namely D3 and lines near A 559, 521, 517, 470, and 

 447, may be expected. In the General Catalogue the nebula is 

 described as "Very bright ; large, round ; very suddenly much 

 brighter in the middle to a nucleiis ; barely resolvable." 



(2) According to Secchi, Vogel, and Duner, this star has a 

 magnificent spectrum of Group II., all of the ten ordinary bands 

 being well visible. The band near D and the one less refrangible 

 (Duner's 2 and 3) are very wide, but the others are relatively 

 narrow, though strongly marked. Duner notices the peculiarity 

 that band 5 (A. 546) is double. This should be further examined ; 

 the apparent duplicity may be simply due to the superposition 

 of a strong line upon the dark fluting of lead. As the star is an 

 exceptionally bright one for this group, comparisons with the 

 bright flutings of carbon should be made, with the object of 

 further confirming the cometary character of this group of stars. 



(3) This is a star which has hitherto been classed with stars 

 like the sun. The usual more detailed observations are required 

 to determine whether the temperature of the star is increasing 

 or decreasing, 



(4) A star of Group IV. (Vogel). If the colour given by Vogel 

 is correct, one would expect the metallic lines to be fairly well 

 developed in this star, and it would probably be no longer 

 classed in Group IV, The stars of this group are usually white 

 or bluish-white, the yellowish-white stars generally falling in the 

 later stages of Group III. or the earlier stages of Group V. 



(5) The colour and spectrum of this variable have not yet 

 been recorded, as far as I can determine, and the approaching 

 maximum of May 5 may therefore afford a good opportunity of 

 observing it. The range of variability is from 8'o to 14*0 in a 

 period of about 219 days. 



(6) As this comet is travelling northwards and is gradually 

 increasing in brightness, it may be well to note a few of the 

 chief points to which attention should be directed in spectro- 

 scopic observations. The positions given are for Berlin mid- 

 night, and are reprinted from Nature, vol. xli. p. 571. 



Observations of the spectrum of a comet at one time only are 

 now of little value, as there can be no doubt that the spectrum 

 is subject to changes with the variations of temperature due to 

 varying distances from the sun. Tlie question now is : What is 

 the precise nature of these chancjes ? From a discussion of all 

 the observations made up to 1888, Prof. Lockyer has laid down 



what he considers to be the most probable sequence ; but as yet 

 there has been no opportunity of testing his views by continued 

 observations of one comet. According to his view, the spectrum 

 of a comet near aphelion is like that of a planetary nebula, con- 

 sisting simply of a bright line near A 500. This, it will be 

 remembered, was observed by Dr. Huggins in the comets of 

 1866-67. As the temperature increases, the spectrum of carbon 

 begins to appear ; at first the low-temperature spectrum (perhaps 

 better known as the spectrum of carbonic oxide) makes its 

 appearance, and afterwards the spectrum of hot carbon (com- 

 monly known as the hydrocarbon spectrum). The principal 

 flutings in the first spectrum are near \ 483, 519, and 561, and 

 those in the second are compound flutings with their brightest 

 maxima near \ 564, 517, and 473. As the temperature goes on 

 increasing, bright flutings of the metals manganese and lead (A 

 558 and 546) are added to those of carbon, the chief effect of 

 their presence being a variation in the appearance of the band 

 near A 564. With a still further increase in temperature, fluting 

 absorptions of manganese and lead replace the corresponding 

 radiations, and apparently shift the position of the citron band 

 from A 564 to 558 or 546, according to the preponderance of one 

 element or the other. At the highest temperatures, which are 

 only attained by comets which approach very close to the sun, 

 bright lines of sodium, iron, manganese, and other substances, 

 appear, as in Comet Wells and the Great Comet of 1882. (For 

 further details, see Roy. Soc. Proc, vol. xlv. p. 189.) 



For comparison spectra, a spirit lamp, and small quantities of 

 magnesium and the chlorides of manganese and lead are all that 

 are likely to be required, unless complete measurements of wave- 

 lengths are attempted. The chief fluting in the spectrum of 

 magnesium will serve for comparison with the line 500. 



Variations in the form of a comet have not yet been associated 

 with spectroscopic changes. A. Fowler. 



Comets and Meteor Streams. — In the cases of the 

 Leonides and Andromede-;, the annexed comet appears to be at 

 the head of the swarms, and Schiaparelli and others have in- 

 ferred from this fact that a comet is broken up by tidal dis- 

 turbances. Other influences besides tidal action may cause it 

 however, and M. Bredichin, in his memoir " Sur les etoiles 

 filantes," showed how meteorites became detached from the 

 central condensation by explosions, and describe orbits that 

 differ according to the value of the initial velocity towards the 

 sun, and the angle made by its direction with the radius vector. 

 In a later communication {Bull. Soc. Iniper. des Naturalistes de 

 Moscou, 1889, No. 4) the form of the orbits generated by ex- 

 plosions in the comet, and their relation to such meteoritic 

 streams as the Leonides and Andromedes, has been investigated. 

 It is noted that in general the less the eccentricity of the gene- 

 rated ellipse, the more clearly marked are periods of maxima in 

 falls of meteors. With the increase of eccentricity the maxima 

 become less marked, and in the case of a parabolic orbit feeble 

 falls occur each year. The regular periodicity of maxima would 

 favour the formation of a meteoritic stream by a single eruption ; 

 in some cases, however, a series of eruptions must have taken 

 place. M. Bredichin thinks that in the Leonid stream a single 

 eruption was excessively preponderant, in the Andromedes a 

 series of eruptions would appear to have occurred. Other cases 

 have also been studied in detail. A meteorite is regarded as a 

 portion of a large comet ejected from the parent mass by an 

 eruption, and an investigation of the number of appearances of 

 bright meteors indicates the connection between them and shoot- 

 ing stars, and, as would be expected, both have maxima when 

 the earth is passing through a meteoritic stream. Although the 

 connection between comets and meteorites is not a matter of 

 doubt, the above investigation demonstrates it from a new point 

 of view. It seems most probable, however, that the disintegra- 

 tion of a meteoritic swarm that has entered our system is caused 

 by tidal disturbances as well as the repulsive action which is the 

 cause of a comet's tail. 



Stellar Proper Motions. — The number of known stars 

 having proper motions is relatively considerable, but they are 

 much dispersed through astronomical records ; M. J. Bossert, 

 however, in the Bulletin Astronomique for March 1890 gives an 

 excellent synoptical table of such stars. Many calculations are 

 facilitated by such a table, showing the elements that may vary 

 the position of a star ; and in a research on the motion of the 

 solar system it is invaluable. All stars are included whose 

 annual motion is o"-5 or more. The list has been culled from 

 every known catalogue and astronomical record, but the results 



